In general, a communication terminal includes an antenna device to transmit and receive electromagnetic waves. Such an antenna device resonates at a specific frequency band to thereby transmit or receive electromagnetic waves of frequencies corresponding to the band. During resonance at the resonant frequency band, the antenna device has a complex impedance and the S parameter thereof rapidly decreases.
To achieve this, for a wavelength λ corresponding to a desired frequency band, the antenna device includes a conducting wire having an electrical length of λ/2 and one end of the conducting wire is open or shorted. The antenna device transmits electromagnetic waves through the conducting wire and the electromagnetic waves form standing waves on the conducting wire, achieving resonance at the antenna device. Here, the antenna device may include multiple conducting wires of different lengths to extend the resonant frequency band.